EQUINE VETERINARY EDUCATION Equine vet. Educ. (2018) 30 (4) 213-224 doi: 10.1111/eve.12624


Review Article


Review of glucocorticoid therapy in horses. Part 2: Clinical use of systemic glucocorticoids in horses


M. Mora Pereira, E. Groover*, A. Wooldridge and F. Caldwell J. T. Vaughan Large Animal Teaching Hospital, Auburn University, Alabama, USA. *Corresponding author email: esg0001@auburn.edu


Keywords: horse; corticosteroids; glucocorticoid; steroids; dexamethasone; prednisolone; triamcinolone


Summary This article is the second in a review series about the use of glucocorticoids to treat medical and musculoskeletal conditions in horses. This segment in the series summarises reported dosages, methods of administration and the efficacy of glucocorticoids for various systemic diseases in equids. The most common use of systemic glucocorticoids reported in the literature for management and treatment of alterations of the respiratory, integumentary, immune and neurological systems are included.


Introduction


Exogenous glucocorticoids have been used to treat a diverse variety of inflammatory conditions in horses due to their potent and rapid effects. The mechanisms of action and the most common glucocorticoids that are used in equine medicine are discussed in a previous review article in this series. The objective of this segment in the series is to summarise reported dosages, methods of administration and the efficacy of glucocorticoids for common systemic inflammatory diseases. The use of glucocorticoids for respiratory, integumentary, immune-mediated and neurological disorders are reviewed.


Respiratory system


Glucocorticoids for recurrent airway obstruction and inflammatory airway disease Recurrent airway obstruction (RAO), also referred to as heaves and equine asthma, is a chronic inflammatory condition of the lower airways, associated with increased mucus production, contraction of the bronchial smooth muscle and thickening of the airway wall. These changes in the lower airways result in overt increased respiratory effort at rest. The triggering factor for the development of RAO is exposure to organic dust present in the horse’s environment (Cornelisse et al. 2004). This condition most commonly affects mature horses, and the signs can be reversed with medical therapy and environmental management (Cou€


etil et al. 2007). Inflammatory airway


disease (IAD) can affect horses of any age, with subtle clinical signs at rest; however, horses often present with exercise intolerance, poor performance and cough (Cou€


etil et al. 2007).


The presence of high eosinophil or mast cell concentrations in the bronchoalveolar lavage fluid (BALF) suggests that aeroallergens might contribute to the development of this condition (Hoffman et al. 1998; Cou€


etil et al. 2007).


Recurrent airway obstruction and inflammatory airway disease are the most common airway conditions in horses in


which glucocorticoids are used for therapy (Ivester and Cou€


etil 2014). The use of glucocorticoids for their anti-


inflammatory effects, together with bronchodilators and environmental changes, have shown to improve chronic lower airway inflammation in many cases (L Cou€


eguillette 2003; etil et al. 2007; Ivester and Cou€ etil 2014). In some horses,


respiratory conditions such as RAO and IAD can be managed successfully with strict environmental changes in order to minimise allergen exposure, but in cases with significant clinical signs, pharmacological therapy is often necessary to accelerate recovery (Cou€ and Cou€


213


etil et al. 2007; Ivester etil 2014). Since inflammation contributes to the


pathogenesis of RAO and IAD, it should be considered the main target of therapeutic intervention (L


eguillette 2003;


Laan et al. 2006). Medications containing glucocorticoids are commonly


delivered by either the parenteral, oral or inhalation routes in horses, and the severity of the condition often determines the route of treatment; horses with severe inflammation may require parenteral administration to achieve adequate results. The severity and possible cause of airway obstruction and inflammation can be primarily assessed by analysis of BALF, but cytological analysis of fluid collected by transtracheal wash (TTW) is also useful. Microscopic evaluation of these samples will show the type and amount of inflammatory cells involved in the process and the presence of microorganisms (L


eguillette 2003; Hewson and


Arroyo 2015). Findings from these diagnostic tests in combination with the clinical examination can determine the treatment of choice. Ideally, before glucocorticoid therapy is utilised, the clinician should determine through physical


examination findings, cytological examination of BALF or TTW fluid, possibly culture of a TTW sample, and complete blood count, whether or not an infectious respiratory problem is present (Cou€


etil et al. 2007; Hewson and Arroyo 2015).


Glucocorticoids may not be recommended if bacterial infection is present or, at minimum, concurrent antimicrobial therapy may be needed.


Parenteral and enteral use Enteral or parenteral routes for glucocorticoid administration are usually more economical than inhalation therapy, and no specialised equipment is required. Parenteral use of glucocorticoids, especially i.v., is recommended for acute and severe airway obstruction in cases of RAO until the clinical signs are controlled enough to be able to change to enteral or inhaled therapy (L


eguillette 2003). Systemic


administration of dexamethasone rapidly improved clinical signs, lung function and percentage of neutrophils in BALF


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